I have a single 20 watt 12 volt halogen puck light in a china display cabinet. The light is fed by a transformer on top of the cabinet that is plugged into a switched receptacle.

About 2 weeks ago my wife said the light did not work. Replaced the bulb with a spare. Still no light. Got out my multimeter and checked the transformer output, no 12 volts. Checked the AC input, 120 volts OK. Conclusion, bad transformer.

Called Home Depot and returned and reordered. Got the replacement yesterday. Exactly the same thing.

Could I have received 2 defective transformers in a row or am I missing something

Any insight would be appreciated.

Julius793

01-25-2012 11:18 AM

Is there any other low voltage stuff you can test to make sure it's not your tester?

rjniles

01-25-2012 11:46 AM

Quote:

Originally Posted by Julius793
(Post 834375)

Is there any other low voltage stuff you can test to make sure it's not your tester?

I was not sure if the output of the transformer was supposed to be AC or DC so I tested my car battery and got the expected 12 VDC and tested my door bell transformer and got 16 VAC.

Looks like my meter is fine.

Note that the transformer in question says it is and electronic transformer, is that meaningful?

zappa

01-25-2012 11:51 AM

Quote:

Originally Posted by rjniles
(Post 834392)

Note that the transformer in question says it is and electronic transformer, is that meaningful?

Not really. Although you may not get accurate voltage measurements of the output. They are switching DC power supplies without any filtering on the output which makes them more AC than DC. Real crappy looking AC.

Julius793

01-25-2012 11:53 AM

Quote:

Originally Posted by rjniles

Note that the transformer in question says it is and electronic transformer, is that meaningful?

Honestly I don't know my boss is the one that usually buys meterial :laughing:

However you should still be getting a reading of some sort.

zappa

01-25-2012 12:03 PM

oooooooOOOOOOOOOoooooooo....I just thought of something. They don't like to operate without a load so that might be the mystery. Measure the resistance of the complete circuit, bulb in socket and wires, right up to where it attaches to the power supply.

zappa

01-25-2012 12:11 PM

What I mean is, if the bulb is good and no bad connections it may start working if you hook it all up.

rjniles

01-25-2012 01:48 PM

Quote:

Originally Posted by zappa
(Post 834424)

What I mean is, if the bulb is good and no bad connections it may start working if you hook it all up.

Tried it and still NG.

Did some more research; that transformer is intended to power a Xenon lamp and I am trying to use it for a Halogen. Is that my problem?

I may just send this one back and buy something that says it is made for halogen low voltage lamps. (I bought this one because it was on closeout- read I'm a cheapskate):(

zappa

01-25-2012 01:59 PM

Quote:

Originally Posted by rjniles
(Post 834515)

Tried it and still NG.

Did some more research; that transformer is intended to power a Xenon lamp and I am trying to use it for a Halogen. Is that my problem?

I may just send this one back and buy something that says it is made for halogen low voltage lamps. (I bought this one because it was on closeout- read I'm a cheapskate):(

It makes no difference at all, should still work. I'm curious, didja measure the resistance of the lamp circuit to make sure everything was ok there? It should be a pretty low resistance reading.

Question....does the new transformer have the same wattage rating as the old one? That could make a difference as these units will not work unless there is about a 50% nameplate load on it.

Yoyizit

01-25-2012 02:20 PM

These things are terrible to troubleshoot and the high current makes perfect connections mandatory.
Test each transformer by directly wiring to a known good 12v lamp, 20 W or more. Repeat each test several times in case there is an intermittent defect somewhere. Don't assume a connector is "connecting" or a wire has continuity.

av-geek

01-25-2012 02:40 PM

If you are running up against the maximum wattage of the transformer, it's over-current protection may be tripping. The only way to reset it is to disconnect the transformer from power and let it sit for about 30 seconds, then plug it back in. When you attempted to operate it with the lamp installed, it may have overloaded, tripped, and then stopped putting out power when you tried to check it with the meter. WHen you put the battery on it, the battery supplied enough power to make it work. this is NOT an advisable way of testing it however. If there was a short in the line, without a fuse. a big lead-acid battery could deliver enough current to quickly heat the wires up above combustion temperatures!

rjniles

01-25-2012 03:40 PM

I have given up.:furious:
I have worked on this thing half the day and I have had it. I tested the lamp and the wire to by connecting to my car battery. I tested the fixture wires, the lamp and the socket for continuity. The transformer is rated for 60 watts and the single puck light has a 20 watt Halogen lamp. For grins and giggles I tried it with a 50 watt halogen, no change. These are G-6.35 bi-pin lamps.

I called Home Depot and got a RMN and am sending it back. I have found another transformer with a magnetic transformer and have ordered it.

Thanks to all those that tried to help:)

mpoulton

01-26-2012 01:18 AM

The output is not DC. It is AC, but at very high frequency (50,000Hz or so). Many multimeters will not read it at all, or will read it very inaccurately on the AC volts setting. The voltage will also be all over the place if there's no load attached. The only good way to test without fancy equipment is using a known-good light bulb.